The present invention relates to a gas turbine power plant with a gas generator, consisting of a compressor, of a combustion chamber and of a turbine coupled with the compressor whose turbine stages consist at least in part of ceramic materials.
The gas generator of a gas turbine power plant serves for the preparation of a compressed working gas which is capable by expansion in a power output turbine or in a thrust nozzle to provide power output. Good efficiencies of the individual components and as high a thermal efficiency as possible are of great significance for as effective as possible an operation of the gas turbine. In order to improve the thermal efficiency, attempts are presently under way to ever increase the turbine inlet temperature. However, in doing so one has encountered the limit as to what metallic materials in the turbine area are capable of withstanding also with intensive cooling by reason of thermal and mechanical stresses. The blade cooling itself thereby even causes an efficiency deterioration because a part of the compressed air has to be branched off and is not available for the working process. Additionally, the cooling medium flow influences the cascade flow in a negative way. In particular in small gas turbines, it is frequently too expensive or impossible to install complex cooling systems. One therefore attempts to manufacture the thermally highest stressed components of ceramic material in order to be able to further increase the temperature without loss-entailing cooling system.
However, serious disadvantages confront the advantages of ceramics, i.e., high temperature resistance, great wear and corrosion resistance, slight density and thermal expansion, which up to now have made the use of these materials appear as very problematical. Among these is a low tensional stressability or loadability, unfavorable fracture behavior by reason of the brittleness and strong scattering of the material quality. The centrifugal force stresses which occur at the required turbine rotational speeds are so large that turbine rotors or turbine blades of ceramic materials have not been successfully used up to now in series applications.
It is known from the DE-OS 24 24 895 to reduce the centrifugal force load or stress of a ceramic gas generator turbine stage in that one constructs this stage with considerably smaller radius. Additionally, one seeks to operate the gas generator with reduced rotational speed. However, as the compressor must produce a certain pressure ratio, this means with reduced rotational speed a larger outer diameter of the compressor rotor. The geometry of the compressor rotor assumes very unfavorable shapes and has, as a consequence thereof, a deterioration of the efficiency of these components.
Additionally, a small and slowly rotating first gas generator turbine stage is not capable to produce the power output which is necessary for the drive of the compressor. For that reason, the lacking power output has to be provided by a series-connected second turbine stage. This second turbine stage which operates at higher rotational speed is coupled with the gas generator by way of a regulatable transmission.
However, notwithstanding a high structural expenditure, this arrangement possesses a low efficiency by reason of the unfavorable compressor operation.
It is therefore the task of the present invention to eliminate by appropriate measures at the gas generator the problems preventing the series utilization of ceramic materials and to operate the compressor and turbine each with optimal rotational speeds and efficiencies.
The solution of the task resides according to the present invention in the combination of the following features:
(a) The turbine consists of more stages than would be necessary from an aerodynamic point of view, however, at least of two stages;
(b) The turbine is coupled with the compressor by way of a transmission providing a speed-up;
By the increase of the number of stages, a smaller energy drop is involved per turbine stage, and the turbine rotational speed can be lowered. By the combination of this multi-stage turbine with a transmission providing a speed-up transmission ratio, the disadvantages of such slowly rotating turbines for the gas turbine, especially for the compressor, can be avoided. By an appropriate selection of the transmission ratio of the transmission, the compressor can be operated at optimal specific rotational speed and good efficiency notwithstanding low turbine rotational speed, whereas at the same time, the advantages of slowly rotating turbines can be utilized. By reason of the reduced velocity level and of the slight gas flow deflection in the turbine, the friction losses and the profile base losses in the cascades are reduced. The gas forces on the blades become smaller and by reason of the lower blade twist, a stress reduction in the profile leading and trailing edge area results. As the stresses of the turbine blades drop considerably thereby, the latter can be made of ceramic materials. As a result thereof, the turbine temperature and therewith the thermal efficiency of the gas turbine can be considerably increased without having to have recourse to a blade cooling system and the losses connected therewith.
According to a further feature of the present invention, the transmission may be constructed as spur gear transmission, Planetary gear transmission or draw means transmission. The advantage results from the construction as gear transmission that the compressor shaft and the turbine shaft have opposite directions of rotation and the gyroscopic couples are cancelled in part. With a planetary gear coaxiality of the two shafts and smaller structural volume would be of advantage whereby input and output can take place by way of every kinematically meaningful combination of inner planetary gear and ring gear. A draw means transmission offers the advantage of a noiseless operation and the elimination of costly lubricating devices for the transmission.
In one embodiment as a shaft output power plant, an output transmission coupled between a power output turbine and an output shaft can be accommodated advantageously in a common housing together with the transmission disposed in the gas generator. The constructive and servicing expenditures, the lubrication supply and the dimensions of the power plant are reduced in this manner.
According to a further feature of the present invention, it is proposed that the turbine shaft of the gas generator and the transmission gear on the turbine side have separate shafts which are connected by way of a clutch. It is thus avoided that vibrations of the turbine are transmitted onto the transmission or vice versa. Additionally, housing deformations are no longer as strongly effective on the rotor. An intermediate shaft may thereby arranged advantageously between the two shafts.